DE19922603A1 e.g. discloses a method and a device for remote reading of a consumption meter or a counter unit, the counter data of which are detected and can be transmitted via a remote data transmission path to a remote reading module or to a reading unit.
The reading unit and the counter unit may be coupled to one another conductively via continuous lines or inductively. Inductive coupling makes it possible, if necessary, to couple a first coupling coil, which is connected to a mobile reading unit, to a stationarily installed second coupling coil, via which counter data can be read out from the counter unit. In the case of conductive coupling, counter data can be transmitted by means of a switched DC voltage signal without a carrier signal. In the case of inductive coupling, a carrier signal is transmitted, which is modulated by means of the counter data to be transmitted. The DC voltage signal or carrier signal output by the reading unit can furthermore be used for remotely supplying the counter unit, if the same does not have its own power supply.
In addition, one or more counter units can also be read by means of one reading unit via a correspondingly configured network. Different network topologies are used, such as star topology, ring topology or bus topology.
Various protocols can be used for transmitting data. The communication protocol can define a plurality of communication layers, which are e.g. structured according to the OSI model.
A transmission standard that is often used for counters is M-bus (short for Meter-bus), which is specified in the series of standards EN13757. Via the M-bus, it is not only possible for counter data to be read out from counters and transmitted to a reading unit, but it is also possible for control commands to be sent to various sensors and actuators within the communication system, in order e.g. to thus control the consumption flow within the supply system remotely.
The M-bus is a hierarchical system, which is controlled by a master, which is connected to one or more slaves via a transmission line. The master is used as a reading unit in this case, which can read data from the slaves, which may be present in the design of the above-described counter unit. The communication between the master and the slaves takes place serially via a transmission line. To transmit data and electrical energy from the master to the slaves, a DC voltage is applied by the master to the transmission line, which is switched between 36 V and 24 V as a function of the data to be transmitted. A logical “1” corresponds to the higher voltage of 36 V, whilst a logical “0” corresponds to the lower voltage of 24 V. The power consumption of the slave is modulated accordingly for data bits which are sent from the slaves to the master. A logical “1” corresponds to a power consumption of 1.5 mA and a logical “0” corresponds to an additional power consumption in the range from 11 to 20 mA. A slight reduction in the voltage results when transmitting a logical “0” because of the bus impedance.
A further transmission method is known, in which the master or the reading unit applies an AC voltage signal or a DC voltage signal to the transmission line, which is interrupted in fixed or variable time intervals, so that time windows result, within which the slave or the counter unit can transmit data to the reading unit.
The monitoring of the data transmission process, e.g. the determination of the time window within which data can be transmitted, takes place in the counter unit by means of a processor, usually by means of a signal processor. High-performance processors, particularly signal processors, are readily able in this case to monitor and control the data transmission process if they do not have to fulfil any other tasks. However, these processors are expensive and require much electrical power during the continuous monitoring of the data streams.
A correspondingly configured power supply must additionally be made available by the reading unit due to the high power losses of the processors.